Knee osteoarthritis (OA) is a leading cause of pain and disability among veterans, and Department of Veterans Affairs health care users are the most severely affected. There is ample evidence that exercise improves pain, function, and other outcomes among patients with knee OA. However, the vast majority of individuals with knee OA are physically inactive. There is clearly a need to develop and implement programs that efficiently and effectively foster regular physical activity and improve key patient-centered outcomes among veterans with knee OA. The objective of this study is to evaluate the effectiveness a novel STepped Exercise Program for Knee OsteoArthritis (STEP-KOA). This will be a randomized controlled trial of n=345 veterans with symptomatic knee OA in two VISN 6 sites, with participants assigned to two study arms: STEP-KOA and Arthritis Education Control (AE). STEP- KOA will begin with three months of access to a low-resource internet-based exercise training program that uses patient-specific information to determine and deliver an appropriate personalized exercise plan (Step 1). Participants who do not meet response criteria for clinically meaningful improvement in pain and function after three months of Step 1 will additionally receive telephone calls from an exercise counselor for three months, to facilitate adherence and address barriers to physical activity (Step 2). Participants who still fail to meet response criteria after Step 2 will receivein-person physical therapy visits, which address specific functional impairments and further tailor exercise recommendations (Step 3). Outcomes will be assessed at baseline, 3 months, 6 months, and 9 months (primary outcome time point). Veterans in the AE group will be offered participation in STEP-KOA after completing study assessments. The primary outcome will be the Western Ontario and McMasters Universities Osteoarthritis Index (WOMAC), a measure of lower extremity pain, stiffness and function. The secondary outcomes will be objective measures of physical function. The main study analyses will compare the STEP-KOA intervention to the AE control condition at follow-up time points. We will also evaluate patient characteristics associated with the need for progression to each Step and will conduct a cost-effectiveness analysis of STEP-KOA. This stepped exercise intervention is matched with patient needs, and it also provides the VA with a potential approach for focusing limited physical therapy resources toward patients who do not respond adequately to initial, less resource intensive and costly strategies to improve physical activity and related outcomes.